Electrodes For Oxygen Evolution Reaction Research Articles

Controllable synthesis and super electrochemical stability of copper phosphide (Cu3P) nanosheets catalyst in nearly neutral electrolyte

The catalytic activity and stability of cost-effective and highly efficient bifunctional electrocatalysts are crucial for electrochemical water splitting. However, the use of strongly alkaline or acidic electrolytes, which are commonly employed, poses environmental concerns. Therefore, the development of efficient electrocatalysts that can operate stably in neutral or near-neutral electrolytes holds significant importance. In this study, a self-supporting Cu3P/NF electrode was fabricated using a two-step method, wherein metal phosphide Cu3P was grown on a nickel foam (NF) substrate. Notably, the Cu3P/NF electrode exhibits an unexpected enhancement in electrochemical activity and stability when operated in an electrolyte consisting of CuSO4 and Na2CO3. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on the Cu3P/NF electrode require overpotentials of 131 mV and 230 mV, respectively, to achieve a current density of 10 mA cm−2 and 50 mA cm−2. Moreover, the stability of the Cu3P/NF electrode for HER and OER is improved by 90.22 % and 74.54 %, respectively, with the inclusion of CuSO4 in the Na2CO3 electrolyte. The improved catalytic performance and stability of Cu3P/NF electrode with the addition of CuSO4 can be attributed to the prevention of Cu + oxidation through Cu2+ and the formation of a local H+ adsorption electric field by the SO42− electron cloud. These factors contribute to the enhanced electrocatalytic activity and stability of Cu3P. This work expands the efficient utilization of electrocatalysts in near-neutral electrolytes, which is of great value for the widespread application of electrocatalysts and environmental protection.

In-situ reconstruction of rock-like 3D hierarchical MIL-53(Fe) self-supporting electrode with oxygen vacancy induced ultra-long stable and efficient water oxidation

The exploitation of efficient, stable and cheap electrocatalyst for oxygen evolution reaction (OER) is very significant to the development of energy technology. In this study, Fe-based metal–organic frameworks (MIL-53(Fe)) self-supporting electrode with a 3D hierarchical open structure was developed through a semi-sacrificial strategy. The self-supporting electrode exhibits an excellent OER performance with an overpotential of 328 mV at 100 mA cm−2 in 1 M KOH, which is superior than that of IrO2 catalyst. Importantly, the optimized self-supporting electrode could operate at 100 mA cm−2 for 520 h without visible decrease in activity. It was also found that the structure of MIL-53(Fe) was in-situ self-reconstructed into oxyhydroxides during OER process. However, the 3D hierarchical open structure assembled with nano-microstructures kept well, which ensured the long-term stability of our self-supporting electrode for OER. Furthermore, density functional theory (DFT) calculations reveal that the FeOOH with rich oxygen vacancy transformed from MIL-53(Fe) plays a key role for the OER catalytic activity. And, the uninterrupted formation of oxygen vacancy during OER process ensures the continuous OER catalytic activity, which is the original source for the ultra-long stability of the self-supporting electrode toward OER. This work explores the way for the construction of efficient self-supporting oxygen electrodes based on MOFs.

Deep Reconstruction of Mo‐based OER Pre‐Catalysts in Water Electrolysis at High Current Densities

AbstractEvaluating the dynamic structural reconstruction processes of transition metal‐based oxygen evolution reaction (OER) catalysts at industrial current densities in a membrane electrode assembly (MEA) configuration of an anion exchange membrane (AEM) electrolyzer is required for the practical application of OER electrodes in AEM‐type next‐generation electrolyzers. This study unveils the deep reconstruction phenomenon of a Mo‐containing OER catalyst anode during electrolysis at high current densities. A complete reconstruction of the catalyst due to selective Mo‐leaching is inevitable during high current operation and thereby new catalytic surfaces of the Mo‐containing Ni‐based electrodes for sustainable water electrolysis are exposed. The reconstruction was confirmed by ex situ and in situ surface characterization techniques. A scalable route for electrode fabrication demonstrated and it is shown that the reconstruction mechanism of the catalyst leads to a more sustainable operation of the electrolyzer at high current densities.

Metal-Organic-Framework-Based Nanoarrays for Oxygen Evolution Electrocatalysis.

The development of highly active and stable electrode materials for the oxygen evolution reaction (OER) is essential for the widespread application of electrochemical energy conversion systems. In recent years, various metal-organic frameworks (MOFs) with self-supporting array structures have been extensively studied because of their high porosity, abundant metal sites, and flexible and adjustable structures. This review provides an overview of the recent progress in the design, preparation, and applications of MOF-based nanoarrays for the OER, beginning with the introduction of the architectural advantages of the nanoarrays and the characteristics of MOFs. Subsequently, the design principles of robust and efficient MOF-based nanoarrays as OER electrodes are highlighted. Furthermore, detailed discussions focus on the composition, structure, and performance of pristine MOF nanoarrays (MOFNAs) and MOF-based composite nanoarrays. On the one hand, the effects of the two components of MOFs and several modification methods are discussed in detail for MOFNAs. On the other hand, the review emphasizes the use of MOF-based composite nanoarrays composed of MOFs and other nanomaterials, such as oxides, hydroxides, oxyhydroxides, chalcogenides, MOFs, and metal nanoparticles, to guide the rational design of efficient OER electrodes. Finally, perspectives on current challenges, opportunities, and future directions in this research field are provided.

Highly Efficient Cobalt Sulfide Heterostructures Fabricated on Nickel Foam Electrodes for Oxygen Evolution Reaction in Alkaline Water Electrolysis Cells

Non-noble metal electrocatalysts for the oxygen evolution reaction (OER) have recently gained particular attention. In the present work, a facile one-step electrodeposition method is applied in situ to synthesize cobalt sulfide nanostructures on nickel foam (NF) electrodes. For the first time, a systematic study is carried out on the impact of the Co/S molar ratio on the structural, morphological, and electrochemical characteristics of Ni-based OER electrodes by employing Co(NO3)2·6 H2O and CH4N2S as Co and S precursors, respectively. The optimum performance was obtained for an equimolar Co:S ratio (1:1), whereas sulfur-rich or Co-rich electrodes resulted in an inferior behavior. In particular, the CoxSy@NF electrode with Co/S (1:1) exhibited the lowest overpotential value at 10 mA cm−2 (0.28 V) and a Tafel slope of 95 mV dec−1, offering, in addition, a high double-layer capacitance (CDL) of 10.7 mF cm−2. Electrochemical impedance spectroscopy (EIS) measurements confirmed the crucial effect of the Co/S ratio on the charge-transfer reaction rate, which is maximized for a Co:S molar ratio of 1:1. Moreover, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) were conducted to gain insights into the impact of the Co/S ratio on the structural and morphological characteristics of the electrodes. Notably, the CoxSy@NF electrocatalyst with an equimolar Co:S ratio presented a 3D flower-like nanosheet morphology, offering an increased electrochemically active surface area (ESCA) and improved OER kinetics.

Optimization of NiFe oxygen evolution reaction catalytic electrode based on characterization of onset potential distribution

Lower onset potential and uniform distribution of catalytic performance are crucial for catalytic electrodes. This study presents a method for characterizing the spatial distribution of the initial potential on the surface of the oxygen evolution reaction (OER) catalytic electrode using total internal reflection imaging (TIRi). By applying linear sweep voltammetry (LSV) with incremental positive potential to the electrode, the surface of the electrode generates micro-to-nanometer-sized O2 bubbles during the initial phase of OER, resulting in an increase in light intensity and a decrease in the effective refractive index (RI). By establishing the relationship between light intensity and potential, the spatial distribution of the OER onset potential can be quantified, enabling direct visualization of the electrode's surface and its catalytic activity. Furthermore, we applied the TIRi method to assess the influence of different substrates and electrodeposition conditions on the catalytic activity, repeatability, and durability of NiFe catalytic electrodes. This research contributes to the evaluation of various electrode deposition methods for large-scale catalytic electrodes and the rational manufacturing of efficient OER electrodes in industrial energy devices, promoting the development of the hydrogen energy field.

Self-supported iridium integrated leaf-shaped Fe3O4 columnar arrays toward highly efficient oxygen evolution at industrial-grade current density

The sluggish kinetics for oxygen evolution reaction (OER) significantly impede the practical applications of electrocatalytic water splitting technology for renewable energy source. The facile design of self-supporting electrocatalysts with high activity and stability for OER catalysis at industrial-grade current density is of paramount significance to mitigate the above bottlenecks. We report herein the construction of iron foam (IF) self-supported Ir-magnetite (Ir-Fe3O4/IF-T-x) electrode via galvanic replacement between IrCl62− ions and Fe2+ in Fe3O4 nanosheet arrays, which is simply synthesized by annealing IF in air and subsequent thermal treatment in reducing atmosphere. Such pre-treatment enables the growth of leaf-like Fe3O4 nanosheet arrays with rich Fe2+ species and oxygen defects, which facilitate the depositing of Ir on the surface of nanosheet arrays and thereby promote the electrochemical OER performance in basic electrolyte. Impressively, the optimized Ir-Fe3O4/IF-400-2 delivers the highest electrocatalytic activity with a low overpotential of 316 mV to obtain industrial-grade current density of 500 mA cm−2 for alkaline OER. Meanwhile, the catalyst still shows good long-term stability after 36 h V-t test at 100 mA cm−2. This study offers a simple and efficient pathway to prepare self-supporting electrode for alkaline OER at industrial-grade current density.

Wettability and heterojunction synergistic interface optimization guided Co doped MoS2/Ni3S2-GO/NF catalytic electrode to boost overall water splitting

Rationally designing cost-efficient, high-activity and durable electrocatalysts are used for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is sense to solve the energy crisis and conversion. Herein, the heterostructure superwetting Co–MoS2/Ni3S2-GO/NF electrode is successfully fabricated by a typical hydrothermal reaction and it's electrocatalytic performance is also systematically studied. Thanks to the establishment of Co doped MoS2/Ni3S2 heterojunction, the improvement conductivity by the addition of graphene oxide (GO), and the superhydrophilicity and superaerophobicity of microstructure, the electrode shows excellent catalytic characteristics and only need an overpotential of 123 mV for OER and 161 mV for HER to reach 10 mA cm−2 and can work steadily for 15 h in alkaline solution. Remarkebly, the superwetting heterojunction electrode demonstrated excellent overall water decomposition ability when used as bifunctional electrocatalyst in 1.0 M KOH and only 1.47 V is required to achieve 10 mA cm−2. Density functional theory (DFT) calculations show the constructed heterogeneous interface and Co doping are conducive to optimizing the chemisorption energy of hydrogen-containing intermediates. This work provides a new way of thinking that collaborative optimization of electrode structure and surface wettability regulation to increase the active area of reaction and accelerate the bubble release toward high-performance OER and HER electrodes.

Sulfidation of CoCuOx Supported on Nickel Foam to Form a Heterostructure and Oxygen Vacancies for a High-Performance Anion-Exchange Membrane Water Electrolyzer.

Anion-exchange membrane water electrolyzer (AEMWE) is attracting attention for hydrogen production owing to its ability to employ nonprecious metal catalysts and high energy conversion efficiency. Spinel-structured transition metal oxides exhibit excellent potential in oxygen evolution reaction (OERs). Nevertheless, the research on highly active and durable spinel-structured electrodes for the anodic OER of AEMWE is deficient. Herein, a self-supported S-CoCu oxide/nickel foam (S-CoCuOx/NF) anode was synthesized through a two-step method (electrodeposition and sulfidation). The formation of abundant oxygen vacancies and heterostructure collaboratively enhances the electron and mass transfer, resulting in an overpotential of 313 mV at 100 mA cm-2 for OER. For the lab-scale AEMWE system with the S-CoCuOx/NF anode, a current density of 1 A cm-2 was obtained at 1.87 V (cell voltage) with high durability for 110 h (1 A cm-2) at 60 °C. The results will provide insights into developing the spinel structure-derived anode for high-performance AEMWE.

Elucidation of nickel–iron chloride/oxychloride as a precatalyst for oxygen evolution reaction

This study unravels nickel–iron chloride/oxychloride as a unique precatalyst for oxygen evolution reaction. Chloride/oxychloride layers are electrodeposited on a permalloy surface upon sodium chloride etching to prepare the precatalyst. After chloride etching for 20 cycles (NiFe-NaCl-20) in NaCl, the oxygen evolution reaction (OER) activity of the pristine permalloy (B-NiFe) in 1.0 M KOH electrolyte is highly enhanced than those of the alloys eroded for 10 (NiFe-NaCl-10) and 30 cycles (NiFe-NaCl-30). In addition, the heterogeneous chloride/oxychloride electrode surfaces are transformed into active hydroxide/oxyhydroxide in KOH. Consequently, the as-prepared NiFe-NaCl-20 electrode required a low overpotential of 246 mV to achieve a current density of 10 mA cm−2 compared to the other investigated electrodes. The enhanced performance may be attributed to the formation of numerous high-valent chloride/oxychloride species on the NiFe-NaCl-20 electrode surface. These results indicate that nickel–iron chloride/oxychloride is a competent precursor for developing an active OER electrode.

Two-step electrodeposition to achieve durable IrOx electrode with a semi-crystalline structure for efficient OER

The Development of highly catalytically active and stable anodes for oxygen evolution reaction (OER) in acidic media remains a great challenge. Herein, we proposed a two-step electrodeposition method to optimize an amorphous electrodeposited IrOx electrode (eⅡ-IrOx/Ti). The introduction of a pre-deposition layer, prepared by triangular wave electrodeposition, contributes to the enhancement of surface oxygen vacancies, resulting in a semi-crystalline structure. Compared to directly potentiostatic electrodeposited IrOx electrode (e-IrOx/Ti) and industrially thermally decomposed IrO2 electrode (IrO2–Ta2O5/Ti) at the same iridium loading level, eⅡ-IrOx/Ti exhibited superior OER performance, with a Tafel slope of 52.85 mV/dec and an overpotential as low as 218 mV at 10 mA/cm2. Moreover, eⅡ-IrOx/Ti demonstrates remarkable stability while continuously catalyzing OER at 250 mA/cm2 for 100 h, with little performance decay and a stability number of 3.397 × 106 (comparable to crystal IrO2). The semi-crystalline structure of eII-IrOx/Ti, rich in oxygen vacancies, facilitates the synergistic effect of amorphous and crystalline phases, indicating the potential of electrodeposited IrOx electrodes for sustained and efficient OER in acidic environments.

V2O5-Fe3O4/rGO Ternary Nanocomposite with Dual Applications as a Dye Degradation Photocatalyst and OER Electrocatalyst.

The design and synthesis of structured nanomaterials with dual properties have always been highly attractive in various fields, especially in the reduction of environmental pollution as well as the generation of renewable energy. In this study, the synthesized ternary V2O5-Fe3O4/rGO nanocomposite was investigated to evaluate both the photocatalytic and electrocatalytic activities for the removal of methylene blue (MB) dye under UV/visible light radiation and oxygen evolution reaction (OER), respectively. The magnetized V2O5-Fe3O4/rGO nanocomposite is characterized by TEM, FE-SEM (with coupling by elemental mapping), EDS, XRD, FTIR, Raman, PL, DRS, and UV-vis analyses. The obtained results show that the graphene oxide substrate is decorated very well using Fe3O4 and V2O5 nanoparticles and converted to reduced graphene oxide (rGO). Furthermore, the V2O5-Fe3O4/rGO nanocomposite is considered as an active catalyst material to modify the commercial glassy carbon electrode for OER using linear sweep voltammetry (LSV). The photocatalytic activity of this novel nanocomposite revealed 89.2% (kobs = 1.7 × 10-2 min-1) and 76% (kobs = 8.3 × 10-3 min-1) degradation efficiencies of MB dye under UV and visible light irradiation at room temperature, respectively, and the surface area of the V2O5-Fe3O4/rGO nanocomposite was examined to be 705.8 cm2/g by N2 adsorption-desorption isotherms. In addition, electrochemical measurements determined the best OER performance of the ternary nanocomposite with the lowest overpotential (458 mV) and Tafel slope (132 mV dec-1) compared to the rGO substrate, Fe3O4, V2O5 nanoparticles, and binary nanocomposites. This work shows much enhancements in both photocatalytic and electrocatalytic activities due to the synergistic effect of the decorated GO support with V2O5 and Fe3O4 nanoparticles.

In-situ surface reconstructed NiOOH/Ni-ZnSe composite electrocatalysts with high activity toward oxygen evolution reaction in alkaline media

Fabricating long-durability and high-activity electrodes for oxygen evolution reaction (OER) in alkaline electrolyte is of great importance for practical water electrolysis. In this work, we develop a composite catalyst composed of Ni-doped zinc selenide nanoparticles embedded in nitrogen-doped amorphous carbon framework (denoted as Ni-ZnSe composite). Concretely, the systematic investigations disclose that the amorphous nickel (oxy)-hydroxide (NiOOH) in-situ formed on the surface of the hybrid catalyst during the OER process is considered as the genuine active centers. This self-reconstructed electrocatalyst (denoted as NiOOH/Ni-ZnSe) only demands small overpotentials of 218, 242 and 292 mV at the 10, 20 and 50 mA cm-2, respectively, as well as low Tafel slope of 56 mV dec-1 in alkaline media. XPS characterization reveals that performance enhancement is attributed to the electronic interaction between Ni-ZnSe and nitrogen-doped carbon (NC) that facilitate interfacial electron transfer, which in turn favors improve the oxygen evolution activity. This work not only enhances the electrocatalytic activity of selenide-based catalyst, but also provides a judicious avenue for developing advanced heterometallic doped catalysts toward OER and beyond.

Electrochemical Analysis of Anion Exchange Membrane Water Electrolyzers (AEMWE)

The increase in deployment of renewable electricity has made green hydrogen production an attractive solution for decarbonizing energy systems. The prominent technologies currently deployed are the proton exchange membrane water electrolyzers (PEMWE) and alkaline water electrolyzers (AWE). The PEMWE technology uses platinum group material (PGM) catalysts, coated onto fluorinated Nafion® polymer membranes and needs specially treated titanium bipolar plates, reaching current densities of greater than 2 A cm-2. The AWE technology, in contrast, uses cheaper materials with a porous diaphragm separator, but the operating current density reaches only <0.5 Acm-2. The anion exchange membrane water electrolyzers (AEMWE) combine the advantages of both the PEMWE and AWE by using hydroxide (OH-) conducting, functionalized styrene-based membranes with non-PGM electrocatalysts, reaching current densities of >1 Acm-2.In this study, a membrane electrode assembly (MEA) consisting of Sustainion® X37-50 Grade RT membranes and non-PGM hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts are fabricated and analyzed for performance. NiFe2O4 (Merk) was chosen as the OER electrocatalyst and spray-coated on the sintered 316L stainless steel fibre (dioxide materials). On the counter side, NiFeCo (USnano) as HER electrocatalyst was spray coated on the molded graphite layer 370 (MGL370- fuelcellstore) porous transport layer. A catalyst loading of 3 mg cm-2 is obtained for both HER and OER electrodes. The fabricated MEA of 1x1cm2 is firstly tested for performance in a inhouse setup, using current density-voltage scans (j-V) using Zahner Zennium X electrochemical workstation. Consequently, electrochemical impedance spectroscopy (EIS) is performed in pseudo-galvanostatic mode. The perturbation amplitude is adjusted such that a linear region of the j-V curve is probed. The fuel electrode and air electrode contributions to the overall MEA performance are distinguishable due to the twin reference electrode configuration. The half cell-MEA contributions are further analyzed by performing parallel impedance measurements between the i) Reference electrode – cathode, ii) Reference electrode - Anode and iii) full-cell operation at predetermined current-density biases. These type of investigation gives deeper insight to the fuel electrode and the air electrode processes. The quality of the EIS spectra is analyzed using Kramers Krönig residual tests.A sensitivity analysis on the MEA is performed by changing impedance-effecting parameters such as temperature, operating current density and potassium hydroxide (KOH) concentration. Further, post-test characterization of the electrode substrates is performed to identify affected parameters through XPS, Raman spectroscopy, SEM-EDX and XRD techniques. The parallel impedance measurements confirms the presence of anodic, cathodic and low-frequency diffusion processes in real time.

Toward Understanding Interfacial Phenomena of Anion Exchange Membrane Water Electrolyzers: Investigating the Role of Electrolyte pH Gradient with Operando Raman Spectroscopy

There is growing industrial appeal of anion exchange membrane water electrolyzers (AEMWEs) to produce hydrogen. A significant challenge remains that AEMWE durability testing is not standardized, and more minute interfacial degradation mechanisms between ionomer, catalyst, membrane, and electrolyte are not well characterized. Of particular interest is the impact of electrolyte selection on the polarization performance. There is a general desire to achieve reliable operation with environmentally obtained saltwater as the electrolyte, although this presents numerous challenges manifesting in typically poor long-term durability. Saltwater presents complexities in determining electrolyzer component interfacial phenomena.Performance of AEMWEs is typically benchmarked with hydroxide or carbonate solutions, therefore providing more direct opportunities to study fundamental mechanisms with regards to interactions between surfaces. Of particular interest is the presence of electrolyte anion concentration gradients that depend on the polarization state of the oxygen evolution reaction electrode (OER). We demonstrated in our early work with operando Raman probing of a custom designed spectroelectrochemical cell that there is initial evidence of spatially resolved anion gradients from the OER electrode surface into bulk electrolyte in a half cell configuration. We hypothesize that local pH changes near an electrode surface may impact the polarization via transport limited ion exchange and the relative overpotential of the overall cell, ultimately leading to an iterative and long-term contribution to decaying cell durability.We continue our work with a series of in-situ Raman experiments with a full cell configuration: OER electrode with PGM free catalyst, hydrogen evolution reaction (HER) electrode with PGM free catalyst, and anion conductive polymer membrane. Both electrodes also contain an ionically conductive polymer, or ionomer, that serves as a binder. By increasing the complexity of the system to match that of an industrially relevant configuration, we aim to probe the spatially resolved pH gradient with both potassium hydroxide and potassium carbonate solutions of varying concentrations. We utilized a custom, 3D printed, flow cell design comprising a sapphire observation window and isolated electrolyte flow chambers.Operando Raman spectroscopy measurements were conducted primarily with potassium carbonate solutions by tracking the spatially resolved changes in relative peak intensity of carbonate and bicarbonate signatures. With regards to the carbonate-bicarbonate equilibrium, we calculate changes in pH as the probe approaches the surface of an electrode. We finally connect our findings to a proposed mechanism for the interfacial phenomena relative to cell durability as a function of concentration changes and operating voltages.

Cobalt vacancy-originated TiMnCoCN compounds with a self-adjusting ability for the high-efficiency acidic oxygen evolution reaction

Oxygen evolution reaction (OER) electrocatalysts in acidic media, except for precious IrO2, have difficulty realizing good electrocatalytic activity and high electrochemical stability simultaneously. However, the scarcity of IrO2 as an acidic OER electrocatalyst impedes its large-scale application in hydrogen generation, organic synthesis, nonferrous metal production and sewage disposal. Herein, we report the design and fabrication of a nanoporous TiMnCoCN compound based on the nanoscale Kirkendall effect, possessing an intriguing self-adjusting capability for the oxygen evolution reaction (OER) in a 0.5 M H2SO4 solution. The nanoporous TiMnCoCN compound electrode for the acidic OER displays a low overpotential of 143 mV for 10 mA cm−2 and exhibits no increase in potential over 50,000 s, which is ascribed to the self-adjusting ability, Carbon/nitrogen (C/N) incorporation and nanoporous architecture. The concentration of inert TiO2 on the reconstructed surface of the compound can self-adjust with the change in OER potential via a cobalt-dissolved vacancy approach according to the stabilization requirement. In this work, the self-reconstruction law of surface structure was discovered, providing a novel strategy for designing and fabricating nonnoble OER electrocatalysts with superior catalytic performance and robust stability in acidic media.

Highly Disordered Fe-Doped CeO2 with Oxygen Vacancies Facilitates Electrocatalytic Water Oxidation

The practical application of electrocatalytic water splitting is hindered by the sluggish anodic oxygen evolution reaction (OER), where the exploration of efficient and stable electrocatalysts toward water oxidation remains a great challenge. Herein, we report an active iron-doped ceria (FeOx/CeO2) catalyst with a highly disordered feature decorated on three-dimensional (3D) nickel foam, which can directly serve as the superior OER electrode in alkaline media. The highly disordered Fe-doped CeO2 catalyst displays remarkable OER performance with a low overpotential of 252 mV to achieve 10 mA cm–2, a small Tafel slope of 45 mV dec–1, and long-term durability for at least 48 h with a stable structure. The superior OER activity of FeOx/CeO2 is attributed to the lattice oxygen activation mechanism facilitated by its disordered structure as well as the high electrochemical surface area. This study provides valuable insights into the rational design of efficient OER catalysts through tailoring the catalyst structure and reaction pathway.

Self-supported amorphous phosphide catalytic electrodes for electrochemical hydrogen production coupling with methanol upgrading

Efficient catalytic electrodes for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) are pivotal for massive production of green hydrogen from water electrolysis, and the further replacement of kinetically sluggish OER by tailored elecrooxidation of certain organics is a promising way to co-produce hydrogen and value-added chemicals via a more energy-saving and safer manner. Herein, amorphous Ni-Co-Fe ternary phosphides (NixCoyFez-Ps) with different Ni:Co:Fe ratios electrodeposited onto Ni foam (NF) substrate were served as self-supported catalytic electrodes for alkaline HER and OER. The Ni4Co4Fe1-P electrode deposited in solution at Ni:Co:Fe ratio of 4:4:1 displayed low overpotential (61 mV at −20 mA cm−2) and acceptable durability for HER, while the Ni2Co2Fe1-P electrode fabricated in deposition solution at Ni:Co:Fe ratio of 2:2:1 showed good OER efficiency (overpotential of 275 mV at 20 mA cm−2) and robust durability, the further replacement of OER by anodic methanol oxidation reaction (MOR) enabled selective production of formate with 110 mV lower anodic potential at 20 mA cm−2. The HER-MOR co-electrolysis system based on Ni4Co4Fe1-P cathode and Ni2Co2Fe1-P anode could save 1.4 kWh of electric energy per cubic meter of H2 relative to mere water electrolysis. The current work offers a feasible approach to co-produce H2 and value-upgraded formate via an energy-saving manner by rational design of catalytic electrodes and construction of co-electrolysis system, and paves the way for cost-effective co-preparation of more value-added organics and green hydrogen via electrolysis.

Activation stainless steel with electrochemical etching-hydrothermal as an efficient and stable alkaline water oxidation electrode

Stainless steel (SS) has great potential to become an efficient oxygen evolution reaction (OER) catalytic material, but an effective activation method is still lacking. Here, an electrochemical etching-hydrothermal activation strategy is proposed to turn SS into an efficient and stable OER electrode, which can deliver high current density of 300 mA cm−2 with only 314 mV, as well as offers a low Tafel slope of 30 mV dec−1. The catalytic phase formed by the activation has a low surface Ni/Fe ratio and completely disobeys the traditional “Fe-effect” activity trend. The performed O–K edge X-ray adsorption spectra revealed that the high valence states of Ni sites with modified electronic structure may be responsible for the enhanced OER performance. More importantly, the assembled overall water-splitting cell showed that it can withstand long-term durability of 100 h at an ultra-high current density of 2 A cm−2. The strategy presented here could yield an opportunity to convert SS into an efficient and robust catalyst for alkaline water oxidation and is expected to lead to more promising ones due to the diverse composition of SS.

A porous TiC supported nanostructured complex metal oxide ceramic electrode for oxygen evolution reaction

Developing low-cost and high-performance electrodes with a customized size is greatly demanded to satisfy the industrial requirement of electrochemical water splitting. To meet this challenge, a novel binder-free electrode consisted of perovskite Sr2Fe1.4Ni0.1Mo0.5O6-δ (SFNMO) nanofibers or spinel NiCo2O4 (NCO) nanosheets tightly bonded on a porous TiC substrate has been developed to catalyze the oxygen evolution reaction in alkaline water electrolysis. The optimal SFNMO/TiC electrode requires a stable overpotential of ∼380 mV to achieve a current density of 30 mA cm−2 within 20 h of operation. The competitive OER performance of such electrode can be attributed to its unique large finger-like straight pore structure, which favors the mass transfer of electrolyte solution as well as produced oxygen bubbles. Furthermore, the strong adhesion between metal oxide catalysts and TiC substrate is derived from the interfacial reaction (form a TiCxOy solid solution), thus lowering the contact resistance of catalyst/substrate interface and promoting the charge transfer kinetics of electrodes, which leads to an outstanding catalytic performance.